Josh Harder, second from right, the Democratic candidate for the California 10th Congressional District, talks with supporters, Ceres High students Matthew Ochoa, left, and Elizabeth Lopez, second from left, in Modesto, Calif. Harder was joined by California Congressional Rep. Pete Aguilar, Southern Californian Democrat, who came to campaign with Harder in his attempt to unseat incumbent Republican Rep. Jeff Denham in the November election.

Rep. Jeff Denham, R-Calif., speaks at a rally against a proposal by state water officials to increase water flows for the lower San Joaquin River to protect fish, at the Capitol, in Sacramento, Calif. Denham is being challenged by Democrat Josh Harder for the California 10th Congressional District seat in the November election.

November 14, 2018

Harder, 32, a venture capitalist, had anchored his campaign to Denham's vote against the Affordable Care Act, while arguing that he would push for universal health care in Congress. He also argued that Denham and other Washington Republicans ignored poverty and health care in the agricultural 10th District in California's Central Valley.

"Washington is broken because our leaders have put party over country. I pledge that I will always put this community before anything in Washington," Harder said in a statement. As ballot-counting continued, Democrats gained ground in two undecided House races in Orange County, California, raising the possibility of a Democratic sweep of four closely contested congressional races in the one-time Republican stronghold.

In the 45th District in Orange County, Democrat Katie Porter jumped into a 261-vote lead over Republican Rep. Mimi Walters, after trailing the incumbent since Election Day. And in the 39th District, anchored in Orange County, Democrat Gil Cisneros tightened the gap with Republican Young Kim.

Earlier, Democrats claimed the seats of Republican Reps. Dana Rohrabacher in the county's 48th District and retiring Darrell Issa in the 49th District, which cuts through the southern end of the county.

With votes continuing to be counted, Harder's edge has grown after Denham grabbed a slim lead on Election Day. After the latest update, Harder had a 4,919-vote lead out of about 185,000 votes counted, a margin too large for the congressman to overcome with remaining votes.

Denham's campaign did not immediately respond to a request for comment. The 51-year-old Denham had depicted Harder as a liberal, Silicon Valley insider whose values were more closely aligned with House Democratic leader Nancy Pelosi than a district known for producing cherries and almonds. An ad he posted on Twitter labeled Harder "extreme."

The contest was one of a string of showcase battles in California in Republican districts that were targeted by Democrats after Hillary Clinton carried them in the 2016 presidential election. For state Republicans, Denham's defeat marked another setback in a state where the party has been drifting toward irrelevance for years. Democrats hold every statewide office, a supermajority in both chambers of the Legislature and a 3.7-million advantage in voter registrations.

With Harder's win, Democrats will hold at least a 43-10 edge in California U.S. House seats. Denham had proved a durable politician in a district 80 miles (129 kilometers) east of San Francisco with a Democratic registration edge. The former legislator first elected to the House in 2010 is known for his involvement in water issues vital to agriculture. In a tilt to his district's heavy Hispanic population, he pushed Congress to consider a pathway for citizenship for hundreds of thousands of immigrants who came to the U.S. as children and stayed here illegally.

Denham won by 3 percentage points in 2016. The race this year attracted a torrent of campaign dollars: Harder pulled in over $6 million and Denham, $4.5 million. At least 26 outside groups spent another $10 million trying to influence the race, according to California Target Book, which analyzes campaigns.

Denham attributed the close race to money pouring in from outside the district. But he became another victim in a year when Democrats regained control of the House. Other Republican incumbents in California to lose this year include Rep. Steve Knight in the 25th District, north of Los Angeles.

President Donald Trump was a factor in the GOP losses. He lost California by over 4 million votes in 2016, and many voters saw an opportunity to send a message to Washington when they voted for Democrats.

California is home to the so-called Trump "resistance," which has stood in opposition to his policies on the environment and immigration. Harder, a technology investor who was born and raised in the district, said voters were looking for a check against Trump policies that have "made things worse for most people in this community."